A second corn earworm-budworm moth flight and pyrethroid resistance, a perfect storm

As predicted, we are in the midst of a second flurry of corn earworm and tobacco budworm moth activity. Some black light traps are catching even higher numbers than during the first flight. Moths are flushing from peanut, cotton and soybean fields. Each crop is presenting a different scenario in terms of risk to infestation and potential crop damage. I can almost guarantee that peanut and soybean fields will be re-infested with worms, and there is a very good possibility that the infestation will be a mix of both species.

PEANUTS almost never suffer economically from worm feeding, but growers will likely not tolerate the worms and tank mix some insecticide with a planned fungicide application.

SOYBEANS are a different story. This next influx of worms will coincide with pod development and fill. Many fields that have been drought stressed are getting some rain and plants are reflowering which makes them highly attractive to moths. I think pod thresholds will be met or exceeded in many fields and many will need to be re-sprayed. Most of these fields have already been treated, but in my opinion, and in the opinion of other soybean entomologists, no product offers more than about 7 days residual activity so any field treated more than 7 days ago will be completely vulnerable to worms. Another piece of the puzzle is the continued high pyrethroid resistance levels of corn earworm. As of this week, we have tested 1,903 moths and survivorship has climbed back to over 40% (see the attached figure). One sample this week reached 56%. Is this resistance level increasing because many of these moths are from the worms that ‘escaped’ the earlier pyrethroid sprays? Seems logical. The best control will need to incorporate a non-pyrethroid (Larvin, Lannate, Steward, Tracer, Belt). Another tank mix that seems to be working well where ever it is being used (the Delta states, Tennessee, North Carolina) is to add 6 oz of Orthene to a full pyrethroid rate.

COTTON may be the least attractive and least susceptible to this next influx of worms. The hot, dry weather has pushed cotton to cutout with many bolls already too tough to be damaged by worms. Much of the crop will be ready for defoliation within the next 3 weeks or so.
Without some top growth of new tender flowers, squares or small bolls, young worms will not be able to establish. And even if this top growth does become infested, it represents a very small proportion of the total yield, which makes controlling worms (the cost) a tough decision.
Additional information: cew-cypermethrin-19-aug-2010-ppt

Leave a Reply